The physiologic basis for a wide variation in hand blood flow is the effect of the thermoregulatory shunts on hand vascular resistance. The thermoregulatory shunts are present in the fingers and palms. During thermoregulatory vasoconstriction, these shunts are tightly closed and hand blood flow is primarily determined by nutritional needs. During thermoregulatory vasodilation, the shunts are open and provide a low resistance arterio-venous path. During such vasodilation periods, blood pressure measured invasively at the radial artery may not accurately reflect central aortic pressure because the large increase in blood flow along the brachial and radial arteries leads to a significant pressure gradient from proximal to distal locations in the circulatory system.
There are a number of clinical situations when a patient's blood pressure will be monitored invasively by means of an arterial blood pressure line inserted in the patient's forearm, specifically, in the radial artery. These situations include during surgery; in intensive or critical care units; in cardiac care units; and in surgical recovery units, for example. There are a number of common clinical situations in which problems arise in obtaining accurate arterial blood pressure measurement from the invasive arterial blood pressure line in the patient's forearm due to increased blood flow through the hand, particularly through arterio-venous shunts. These include anesthesia-induced vasodilation, hemodilution, use of potent vasodialtors, sepsis, and hyperthermia. Several of these conditions are present at the termination of cardiopulmonary bypass surgery. The inability to accurately monitor arterial blood pressure at a distal location by invasive means due to the presence of a significant pressure gradient in the aforesaid clinical situations is a problem which has not been addressed in a practical manner to date.
It would be highly desirable to provide a practical and readily controlled method and apparatus for lessening the proximal-to-distal pressure gradient in a patient's circulatory system to a degree wherein distal invasive pressure measurements could be obtained which accurately reflect aortic pressure.